The goal of the proposed reseach is to further understanding of the neural control of locomotion, which must ultimately include a full delineation of its neuronal substrate. We will analyze stepping in the cat, because while its gait has never been analyzed quantitatively, a good deal of knowlege is available concerning the central and peripheral neural pathways of this species. We will be concerned particularly with how central programming provides for rhythmic alternation of the four limbs to produce smooth interlimb coordination. The program will consist of three sequential phases: 1) to gather and synthesize quantitative data for natural movement on a treadmill, 2) to produce some restricted (not incapacitating) movement pathologies by selected surgical interventions into peripheral afferent input, the spinal cord, and the cerebellum, and 3) to re-test on the treadmill in order to quantify the nature and the durability of observed deficits. The re- tests will require retraining to determine the limits of the animals' recovery. It should be emphasized that for every animal experiment we perform a human counterpart exists. Many of the methods that will be used to study normal movement in the cat (joint angles, force measurements footfall patterns as synthesized by computer techniques) are directly applicable to gait analysis for man. In addition, our surgical interventions are not unlike disease-produced movement deficits in man, such as Parkinsonism or cerebellar disorders. Finally, our re-test program will yield valuable clues as to the management of disabilities in general in this area. Some deficits that appear to be massive soon after injury will often dissipate spontaneously with time because of unknown plastic properties of the nervous system. The adverse effects of other lesions may often be alleviated greatly by means of some of the powerful behavioral techniques that already have wide human and clinical applications.